In nuclear power plants or various plants, devices, piping, and the like constructing the plant need to be periodically inspected for checking degradation statuses including material degradation, corrosion tendencies, cracks, and other deficiencies, which can provide a future preventive maintenance plan on the basis of the result to provide, for example, a plan indicative of a maintenance timings or replacement timings of structural members. Generally, there are various types of structural members such as devices and piping constructing the plant depending on their configurations and functions and thus the number of installed structural members is large. Accordingly, in order to prevent failure and damage, it is required to specify parts having tendencies of degradation to provide sophisticated advancing degradation progression prediction to conduct inspection or diagnosis within a period for which the parts have soundness and are in service. This provides maintenance in accordance with the degradation status.
For example, Japanese laid-open patent application publication No. 11-64210 discloses a technology in which a sample pipe for inspection is arranged in a piping system to be periodically removed for inspection to predict degradation statuses including corrosion, deficiency and progression of damage on the basis of the inspection result. The sample pipe is arranged at a location showing a higher possibility of degradation or damaging than other locations in the piping system. Further, Japanese laid-open patent application publication No. 6-255330 discloses a technique in which a ring with a notch formed with a material having a shorter life than a structural member to be inspected is fixed to a part of the structural member. The ring is periodically inspected for predicting the life of the structural member to be inspected.
In the methods of managing maintenance, to increase reliability in degradation prediction of structural members, it is preferable to provide a lot of index members. However, inspection should be completed within a certain period, for example, one month, which limits the number of index members. If an excessive number of index (monitoring) members are installed in comparison with the period, non-inspected index members will exist. This will increase possibility of deficiency.
Then, it may be considered to install index members at locations experimentally showing a high degradation. However, in this case, the prediction may be done on the excessively safe side. Thus, the inspection interval for general structural members will be too short, which increases the cost of the maintenance.